The present invention relates to a magneto-optical information processing method and a magneto-optical information processing apparatus, in both of which information is recorded and erased by utilizing a light induced thermo-magnetic effect and is reproduced on the basis of the magneto-optic effect, and more particularly to the above method and apparatus capable of applying a stable magnetic field to a magnetic recording medium in a recording operation and an erasing operation.
A magneto-optical information storage apparatus is disclosed in, for example, an article entitled "Amorphous thin film disk for magneto-optical memory" by NHK Broadcasting Science Research Laboratories, SPIE, Vol. 329, page 208, Optical Disc Technology, 1982. An apparatus of this kind is made up of a recording/reproducing optical system and an electromagnetic coil, and the electromagnetic coil is disposed so that a recording medium is sandwiched between the electromagnetic coil and a focusing lens. Further, a magneto-optical information processing apparatus generally uses a perpendicular magnetic thin film as the information recording medium, and a recording operation is performed by reversing the direction of magnetization of the magnetic thin film in accordance with information. Further, a reproducing operation is performed by utilizing a phenomenon that the plane of polarization of light incident on the magnetic thin film is rotated depending upon the direction of magnetization of thereof, that is, the magneto-optic effect. In this apparatus, recorded information is erasable or rewritable. In more detail, a recording operation and an erasing operation are performed in such a manner that a portion of the magnetic thin film is heated by a laser beam which is focused on the portion, so that the magnetization at the portion is extinguished, and then an external magnetic field in a desired direction is applied to the portion by an electromagnetic coil, to establish fixed magnetization at the portion, that is, the recording and erasing operations are performed on the basis of a light induced thermo-magnetic effect. However, it is required to make the direction of magnetic field applied in the recording operation opposite to the direction of magnetic field applied in the erasing operation. Further, it is important to reverse the direction of applied magnetic field at high speed. Accordingly, in a magneto-optical information processing apparatus, it is very important how stably an external magnetic field is applied to a magneto-optical recording medium to enhance the processing speed and reliability of the apparatus.